1. Field of the Invention
The present invention relates to a sheet laminator, an image forming apparatus, and a sheet laminating method.
2. Description of the Related Art
Conventionally, various attempts have been made to obtain a glossy photographic-quality image on a recording medium using an image forming apparatus that forms a latent image on a photoconductive member in an image forming unit with laser beams emitted from an optical writing unit, develops the latent image with toner, transfers the obtained toner image to the recording medium conveyed by a paper feeder, and fixes the toner image on the recording medium.
For instance, Japanese Patent Application Laid-open No. 2002-341623 describes a technique that uses special toner to attain a glossy image. According to the technique, a photographic quality can be achieved by uniformly applying transparent toner on an entire surface of a sheet, on which an image has been formed according to a conventional method but not processed by a fixing unit yet, and fixing the toner onto the sheet.
Japanese Patent Application Laid-open No. 2004-191678 describes a technique that uses a special recording medium to obtain a glossy image. According to the technique, a surface of a sheet become uniformly glossy by providing a thermoplastic resin layer on a front face or a back face of the sheet, fixing an image onto the sheet by a conventional method, and applying additional pressure and heat to the sheet.
Japanese Patent Application Laid-open No. 2003-270991 describes a technique that uses a special fixing device to obtain a glossy image. According to the technique, a second fixing unit formed from a highly-smooth belt is provided so that toner having been fixed by conventional fixing (first fixing) is melted for a second time, thereafter cooled, and stripped off. By utilizing smoothness of the belt, a uniform gloss can be obtained.
Japanese Patent Application Laid-open No. H3-50586 discloses a simple technique of simply adopting a transparent film into an image forming apparatus. According to the technique, after a mirror image is formed on a transparent film, a white paper or a white board is affixed to the transparent film in close contact. When viewed from a side of the transparent film, the image attains a high gloss and a high photographic quality.
However, in the technique described in Japanese Patent Application Laid-open No. 2002-341623 the transparent toner is required to be applied to an entire surface at each time, and the transparent toner may blur images. It is also necessary to develop an image forming apparatus dedicated for the technique, and therefore it requires a large-scale development and investment.
The technique described in Japanese Patent Application Laid-open No. 2004-191678 can yield its effect only in combined use with the special fixing device described in Japanese Patent Application Laid-open No. 2003-270991. Accordingly, there are needs for an advanced technique in terms of structure, cost, power consumption, and the like.
In the technique disclosed in Japanese Patent Application Laid-open No. H3-50586; the transparent film is manually brought into close contact with the white sheet or the white board using an adhesive agent or the like. Therefore, image quality may be deteriorated due to imprecise bonding (displacement) or diffuse reflection caused by bubbles trapped therebetween.
Meanwhile, bonding the sheets together as described above involves a problem of entrapment of bubbles between sheets. Particularly, when such an image recording sheet as describe above is used, as a matter of course, irregular reflection is caused by trapped bubbles even if the bubbles are extremely small in size and amount. In some cases, the bubbles can cause the sheet to appear dusty, spoiling an image formed thereon.